The present invention relates to flexible containers for use in the transportation and storage of bulk material. Such a container includes integral lifting loops which are direct extensions of the side walls of the container and which form openings for lifting means.
Containers of the above mentioned type have been in use for some time and have proved to be well suited for several purposes. Usually they comprise a liner of impervious material, and when they are to be filled with free-flowing bulk material the liner is usually first inflated by air. U.S. Pat. No. 4,136,723 shows such a container having bottom flaps crossing each other. The container is preferably equipped with two integral lifting loops having a total width substantially equal to half of the container's circumference such that the lifting loops are formed by all of the longitudinal fibers of the container. By using an apparatus described in Great Britain Patent No. 1,505,583 a filled container can stand upright on the floor without any extra support. Its lifting loops can also hang on a hook or the like before inflation and filling of bulk material. The container is made ready for further transport after filling. This may involve closure of the liner and joining of the lifting loops such that one obtains a suitable loop which easily can be placed on a hook or other lifting means by pressing the lifting loops together and securing them in this position. Joining of the lifting loops to a permanent lifting handle can, however, be carried out before the container is filled with bulk material as described in Norwegian Patent Application No. 830,718 (corresponding to European No. 118,112).
By use of a container with a liner of impervious material, the function of the liner is to protect the bulk material in the container against contamination, and to close the container such that the bulk material therein will not flow out if the container topples, for instance due to incorrect handling. In this connection it should be mentioned that the liner must of course be kept completely watertight until discharge, however, experience shows that the upper part of the liner can easily be damaged by lifting means. The liner often is used just to fulfil this function of preventing the bulk material from flowing out of the container, as several types of bulk material do not need to be protected against contamination.
In certain cases, especially during filling of dusty bulk material in flexible containers having at least one lifting loop, the primary function of the liner is to form a filling spout which is placed tightly around the filling pipe and thereby to prevent dust formation during the filling operation.
The liner represents a relatively large part of the total cost of the container. The use of such a liner, if it is only to prevent the bulk material in the container from flowing out due to incorrect handling or if it is only to be used as a filling spout, is therefore not very economical.
However, several types of bulk material require protection against contamination, and a liner has to be used. When a container having integral lifting loops with or without a permanent lifting handle is used, contaminants entering through the openings in the lifting loops can get into the space between the liner and the outer container. When the container is emptied, the pressure from the bulk material against the liner which keeps it against the outer container's walls ceases, and possible contaminants in such space can follow the bulk material out of the container and contaminate the material when being discharged from the container.
Flexible containers as shown in U.S. Pat. No. 4,136,723, having a squarish bottom construction and where the container is equipped with two integral lifting loops having a total width substantially equal to half of the container's circumference, are well suited for transportation and storage of bulk material without the use of a liner of impervious material if the container is closed just below the lifting loop. A known way of doing this is, for instance, by tying a rope around the container below the lifting loops in the form of a clove hitch or the like.
Such method however has the following disadvantages. This closing operation has to be carried out after the bulk material has been filled into the container, since the rope closes the fill opening of the container, and the capacity of the filling apparatus cannot be fully utilized. When the container is pressed together below the lifting loop, channels easily can be formed in the gathered material so that the container will not necessarily be completely closed. The knot in the rope may slip. The capacity of the container cannot be fully utilized, since its net volume is reduced when the container is lashed below the fill opening.